Gas cylinder - WikiHQ

thumb|right|Industrial compressed gas cylinders used for [[oxy-fuel welding and cutting of steel.]]

A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. Gas storage cylinders may also be called bottles. Inside the cylinder the stored contents may be in a state of compressed gas, vapor over liquid, supercritical fluid, or dissolved in a substrate material, depending on the physical characteristics of the contents. A typical gas cylinder design is elongated, standing upright on a flattened or dished bottom end or foot ring, with the cylinder valve screwed into the internal neck thread at the top for connecting to the filling or receiving apparatus.

Types

Since fibre-composite materials have been used to reinforce pressure vessels, various types of cylinder distinguished by the construction method and materials used have been defined:

Type 1: Metal only. Mostly seamless forged metal, but for lower working pressure, e.g., liquefied butane, welded steel vessels are also used.
Rack – A structure to hold cylinders safely upright or horizontal while in use, for transport, or in storage.

Materials

All-metal cylinders are the most rugged and usually the most economical option, but are relatively heavy. Steel is generally the most resistant to rough handling and most economical, and is often lighter than aluminium for the same working pressure, capacity, and form factor due to its higher specific strength. The inspection interval of industrial steel cylinders has increased from 5 or 6 years to 10 years. Diving cylinders that are used in water must be inspected more often; intervals tend to range between 1 and 5 years. Steel cylinders may continue to be used indefinitely providing they pass periodic inspection and testing.

Filament wound composite cylinders are used in fire fighting breathing apparatus, high altitude climbing, and oxygen first aid equipment because of their low weight, but are rarely used for diving, due to their high positive buoyancy. They are occasionally used when portability for accessing the dive site is critical, such as in cave diving where the water surface is far from the cave entrance. Oxidisers such as oxygen and fluorine will produce a similar effect by accelerating combustion in the area affected. If the cylinder's contents are liquid, but become a gas at ambient conditions, this is commonly referred to as a boiling liquid expanding vapour explosion (BLEVE).

Medical gas cylinders in the UK and some other countries have a fusible plug of Wood's metal in the valve block between the valve seat and the cylinder. This plug melts at a comparatively low temperature (70 °C) and allows the contents of the cylinder to escape to the surroundings before the cylinder is significantly weakened by the heat, lessening the risk of explosion.

More common pressure relief devices are a simple burst disc installed in the base of the valve between the cylinder and the valve seat. A burst disc is a small metal gasket engineered to rupture at a pre-determined pressure. Some burst discs are backed with a low-melting-point metal, so that the valve must be exposed to excessive heat before the burst disc can rupture.

The Compressed Gas Association publishes a number of booklets and pamphlets on safe handling and use of bottled gases.

International and national standards

There is a wide range of standards relating to the manufacture, use and testing of pressurised gas cylinders and related components. Some examples are listed here.

ISO 11439: Gas cylinders — High-pressure cylinders for the on-board storage of natural gas as a fuel for automotive vehicles
ISO 15500-5: Road vehicles — Compressed natural gas (CNG) fuel system components — Part 5: Manual cylinder valve
US DOT CFR Title 49, part 178, Subpart C — Specification for Cylinders
US DOT Aluminum Tank Alloy 6351-T6 amendment for SCUBA, SCBA, Oxygen Service — Visual Eddy inspection
AS 2896-2011:Medical gas systems—Installation and testing of non-flammable medical gas pipeline systems pipeline systems (Australian Standards).
EN 1964-3 – Transportable gas cylinders. Specification for the design and construction of refillable transportable seamless steel gas cylinders of water capacities capacity from 0,5 litre up to 150 litre

Transportation

thumb|250x250px|Transportation of oxygen gas cylinders in special truck in Dnipro, Ukraine.

Gas cylinders are classified by the UN as dangerous goods for transportation purposes (US: Hazardous materials). Selecting the Proper Shipping Name (well known by the abbreviation PSN) is a way to help ensure that the dangerous goods offered for transport accurately represent the hazards.

IATA Dangerous Goods Regulations (DGR) 55th Edition defines the Proper Shipping Name as "the name to be used to describe a particular article or substance in all shipping documents and notifications and, where appropriate, on packagings".

! Hazard class or division

! Identification numbers

! Label codes

! Quantity limitations

| Air, compressed

| 2.2

| UN1002

| 2.2

| rowspan=7 | Passenger aircraft/rail: 75 kg Cargo aircraft only: 150 kg

| Argon, compressed

| 2.2

| UN1006

| 2.2

| Helium, compressed

| 2.2

| UN1046

| 2.2

| Nitrogen, compressed

| 2.2

| UN1066

| 2.2

| Oxygen, compressed

| 2.2

| UN1072

| 2.2, 5.1

| Compressed gas N.O.S. (not otherwise specified) e.g. normoxic and hypoxic Heliox and Trimix

| 2.2

| UN1956

| 2.2

| Compressed gas, oxidising, N.O.S e.g. Nitrox

| 2.2

| UN3156

| 2.2, 5.1

<!--Special provisions: 78, n/a, A14

Packaging (§ 173.***): Exceptions Air 306,307, He 306, O2 306, Non-bulk Air 302 He302, O2 302, Bulk Air 302 He 302, 314 O2 314, 315

Vessel stowage: Location All A

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International air

International Civil Aviation Organization (ICAO) Technical Instructions for the Safe Transport of Dangerous Goods by Air states that provided that pressure in diving cylinders is less than , these can be carried as checked in or carry-on baggage. It maybe necessary to empty the cylinder to verify this. Once emptied, the cylinder valve should be closed to prevent moisture entering the cylinder. Security restrictions implemented by individual countries may further limit or forbid the carriage of some items permitted by ICAO, and airlines and security screening agencies have the right to refuse the carriage of certain items.

Europe

Since 1996 the carriage of dangerous goods legislation of the UK has been harmonized with that of Europe.

Road transport

The 2009 (amended 2011) UK Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations (CDG Regulations) implement the European Agreement Concerning the International Carriage of Dangerous Goods by Road (ADR). Dangerous goods to be carried internationally in road vehicles must comply with standards for the packaging and labelling of the dangerous goods, and appropriate construction and operating standards for the vehicles and crew.

Transport of gas cylinders in a vehicle, for commercial purposes, must follow basic legal safety requirements and, unless specifically exempted, must comply with ADR. The driver of the vehicle is legally responsible for the safety of the vehicle and any load being carried, and insurance for the vehicle should include cover for the carriage of dangerous goods. in the USA is regulated by Code of Federal Regulations Title 49 - Transportation, (abbreviated 49 CFR). A cylinder containing 200 kPa (29.0 psig/43.8 psia) or greater at 20 °C (68 °F) of non-flammable, nonpoisonous compressed gas, and being transported for commercial purposes is classified as HAZMAT (hazardous materials) in terms of 49 CFR 173.115(b) (1). Cylinders manufactured to DOT standards or special permits (exemptions)issued by the Pipeline and Hazardous Materials Safety Administration and filled to the authorized working pressure are legal for commercial transport in the USA under the provisions and conditions of the regulations. Cylinders manufactured outside the USA may be transported under a special permit, and these have been issued for solid metal and composite cylinders with working pressures of up to 300 bar (4400 psi) by several manufacturers.

Commercial transportation of breathing gas cylinders with a combined weight of more than 1000 pounds may only be done by a commercial HAZMAT transportation company. Transport of cylinders with a combined weight of less than 1000 pounds requires a manifest, the cylinders must have been tested and inspected to federal standards, and the contents marked on each cylinder. Transportation must be done in a safe manner, with the cylinders restrained from movement. No special licence is required. DOT regulations require content labels for all cylinders under the regulations, but according to PSI, labelling of breathing air will not be enforced. Oxygen or non-air oxidizing (O2 ≥ 23.5% ) mixtures must be labelled. Private (non-commercial) transport of scuba cylinders is not covered by this regulation.

Empty scuba tanks or scuba tanks pressurized at less than 200 kPa are not restricted as hazardous materials. Scuba cylinders are only allowed in checked baggage or as a carry-on if the cylinder valve is completely disconnected from the cylinder and the cylinder has an open end to allow for a visual inspection inside.

Color coding

thumb|ISO Cylinder Colour Coding for Different (medical) Gases

Gas cylinders are often color-coded, but the codes are not standard across different jurisdictions, and sometimes are not regulated. Cylinder color can not safely be used for positive product identification; cylinders have labels to identify the gas they contain.

Medical gas cylinder color code Indian standard

The Indian Standard for Gas Cylinder Color Code applies to the identification of the contents of gas cylinders intended for medical use. Each cylinder shall be painted externally in the colours corresponding to its gaseous contents.

Permanent markings

The shoulder of the cylinder carries stamp markings providing required information about the cylinder.)

Gas storage tubes

For larger volume, high pressure gas storage units, known as tubes, are available. They generally have a larger diameter and length than high pressure cylinders, and usually have a tapped neck at both ends. They may be mounted alone or in groups on trailers, permanent bases, or intermodal transport frames. Due to their length, they are mounted horizontally on mobile structures. In general usage they are often manifolded together and managed as a unit.

Gas storage banks

thumb|right|Hydrogen storage cylinders in a cascade filling system

Groups of similar size cylinders may be mounted together and connected to a common manifold system to provide larger storage capacity than a single standard cylinder. This is commonly called a cylinder bank or a gas storage bank. The manifold may be arranged to allow simultaneous flow from all the cylinders, or, for a cascade filling system, where gas is tapped off cylinders according to the lowest positive pressure difference between storage and destination cylinder, being a more efficient use of pressurised gas.

Sources

CD-ROM prepared and distributed by the National Technical Information Service (NTIS)in partnership with NOAA and Best Publishing Company

External links

NASA — Safety Standards for Oxygen and Oxygen Handling
Briefing Note: Cylinder valves on high pressure oxygen tanks Date: 6 January 2025